In communications systems, there are a lot of “internal” interfaces between the different Evolved Packet Core (EPC) nodes such as e.g. the Serving General packet radio service Support Node (SGSN), the Mobility Management Entity (MME), the Gateway General packet radio service Support Node (GGSN), the Serving GateWay (SGW), the Packet data network GateWay (PGW) and the Policy and Charging Rules Function (PCRF). The interfaces between these nodes may be referred to as control plane interfaces and they exist in order to e.g. handle the communication between the different nodes.
Some examples of control plane interfaces are:                S3 (between the SGSN and the MME).        S4 (between the SGSN and the SGW).        S5 (between the SGW and the PGW).        S11 (between the SGW and the PGW).        Gn (between the SGSN and the GGSN (excluding the SGSN-SGSN communication)).        Gx (between the PGW and the PCRF).        
These example interfaces may create an example architecture of a communications system 100 as illustrated in FIG. 1. In more detail, FIG. 1 illustrates an exemplary embodiment of a non-roaming architecture for Third Partnership Project (3GPP) access. FIG. 1 shows a User Equipment (UE) 101 served by a Radio Access Network (RAN) node in an E-UTRAN 103. E-UTRAN is short for Evolved-Universal Terrestrial Radio Access Network. The RAN node may be for example a base station, a NodeB, an evolved NodeB (eNode B, eNB), Radio Network Controller (RNC) or any other element capable to communicate with the UE 101. The interface between the UE 101 and the E-UTRAN 103 may be referred to as LTE-Uu.
An MME 108 may be connected to the E-UTRAN 103 via the S1-MME interface. The MME 108 is a Core Network (CN) node having functions such as e.g. Non-Access Stratum (NAS) signalling, Inter CN node signalling for mobility between 3GPP access networks, UE reachability, Tracking Area (TA) list management, PGW and SGW selection, MME selection for handover with MME change etc. S10 is the interface between MMEs 108 for MME relocation and MME to MME information transfer.
Two gateway nodes are seen in FIG. 1, i.e. the SGW 110 and the PGW 115. The SGW 110 and the PGW 115 may be implemented in one physical node or in separate physical nodes. The SGW 110 is the gateway which terminates the interface towards E-UTRAN 103. The interface between the SGW 110 and the E-UTRAN 103 for the per bearer user plane tunneling and inter eNodeB path switching during handover may be referred to as S1-U. The SGW 110 routes and forwards user data packets, while also acting as the mobility anchor for the user plane during inter-eNodeB handovers etc. S11 is the interface between the SGW 110 and the MME 108.
The PGW 115 is the gateway which terminates the SGi interface towards the Packet Data Network (PDN). The PDN is illustrated in FIG. 1 by the Operator's IP Services (e.g. IMS, PSS etc.) 118. IP is short for Internet Protocol, IMS is short for IP Multimedia Subsystem or IM Multimedia core network Subsystem and PSS is short for Packet Switched Streaming. If the UE 101 is accessing multiple PDNs, there may be more than one PGW 115 for that UE 101. Functions of the PGW 115 are e.g. providing connectivity from the UE 101 to external PDNs by being the point of exit and entry of traffic for the UE 101, performing policy enforcement, packet filtering for each user, charging support, lawful interception and packet screening etc. S5 is the interface which provides user plane tunnelling and tunnel management between the SGW 110 and the PGW 115.
The SGSN 120 is responsible for the delivery of data packets to and from the UE's 101 within its geographical service area. One of the SGSN's 120 functions is to provide signaling for mobility between Second Generation/Third Generation (2G/3G) and E-UTRAN 3GPP access networks. 2G/3G access network are exemplified with GERAN 122 and UTRAN 125 in FIG. 1. GERAN is short for GSM EDGE Radio Access Network, GSM is short for Global System for Mobile Communications, EDGE is short for Enhanced Data rates for GSM Evolution and UTRAN is short for Universal Terrestrial Radio Access Network. Some further functions of the SGSN 120 are to handle packet routing and transfer, mobility management (attach/detach and location management), logical link management, and authentication and charging functions etc. S3 is the interface between the SGSN 120 and the MME 108. S4 is the reference between the SGSN 120 and the SGW 110. S12 is the interface between the SGW 110 and the UTRAN 125. In some embodiments, the SGSN 120 and the MME 108 are co-located in one node. In this text, the term MME/SGSN will refer to any one of a standalone MME 108 or a standalone SGSN 120 or a combined MME 108 and SGSN 120 node.
The Home Subscriber Server (HSS) 128 is a subscriber server node similar to the GSM Home Location Register (HLR) and Authentication Centre (AuC). The HSS 128 comprises subscriber-related information (subscriber profiles), performs authentication and authorization of the user, and may provide information about the subscriber's location and IP information. The interface S6a enables transfer of subscription and authentication data for authenticating/authorizing user access to the evolved system between the MME 108 and the HSS 128.
The PCRF 130 is a policy and charging control element node. The PCRF 130 encompasses policy control decision and flow based charging control functionalities, it provides network control regarding the service data flow detection, gating, Quality of Service (QoS) and flow based charging etc. The PCRF 130 may be described as a functional entity which may be a standalone node or a function implemented in another node. The interface Gx provides transfer of (e.g. QoS) policy and charging rules from the PCRF 130 to e.g. a Policy and Charging Enforcement Function (PCEF) in the PGW 115.
Rx is the interface between the PCRF 130 and the Operator's IP Services 118. The Rx interface is used to exchange application level session information between the PCRF 130 and the Application Function (AF) (not shown).
In some embodiments, a communications system may be divided into a radio access network and a core network. The radio access network may be e.g. the E-UTRAN 103 and may comprise a RAN node such as e.g. the base station as described above. Using the exemplary embodiment in FIG. 1, the core network may comprise for example the MME 108, the SGW 110, the PGW 115, the SGSN 120, the HSS 128 and the PCRF 130. The radio access network and the core network may each comprises additional entities not shown in FIG. 1. The core network may be a Packet Switched (PS) core network or a Circuit Switched (CS) core network.
It should be noted that the communication links between the nodes in the communications systems seen in FIG. 1 may be of any suitable kind including either a wired or wireless link. The link may use any suitable protocol depending on type and level of layer (e.g. as indicated by the Open Systems Interconnection (OSI) model) as understood by the person skilled in the art.
Payload may run through at least one of the following nodes:                SGSN 120        GGSN        SGW 110        PGW 115        
Virtualization or Network Functions Virtualization (NFV) is used to separate SoftWare (SW) from HardWare (HW). NFV involves implementing network functions in software that may run on a range of standard hardware and that may be moved to various locations in the network without the need to install new equipment. The NFV is complementary to Software Defined Networking (SDN). SDN allows network administrators to manage network services through abstraction of lower level functionality.